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Two Embryos Form One Child
By Reuters
Contributed by Deeva Vincent
BOSTON
January 15, 1998
Medical researchers in
Britain have found an unexpected risk in the implantation of more than one
fertilized egg in the womb of a woman undergoing in vitro fertilization.
They have found a case in which two embryos, one male and
one female, fused in development to form a single child.
The case, outlined in Thursday's New England Journal of
Medicine, surfaced when an otherwise healthy child was treated
because his left testicle had not descended normally. Surgeons
discovered an ovary and a fallopian tube on the left side.
Otherwise the child, now in school, has developed normally.
In medical terms, the child is known as a chimera, named
after the mythical Greek monster that was part lion, part goat
and part serpent.
The researchers, led by Lisa Strain of the University of
Edinburgh, said the standard practice of implanting more than
one embryo during in vitro fertilization made it possible for
the two embryos to fuse.
``The observation of chimerism after in vitro fertilization
should therefore be taken seriously,'' they said. Such phenomena
can happen naturally, but it is very rare, so rare as to
''suggest a causal link to the in vitro fertilization,'' they
said.
There may be more cases of chimerism than people realize,
the Strain team speculated, because fusions between two male
embryos or two female embryos would probably be missed since the
baby would show no sex organ abnormalities.
The risk of chimerism has risen in recent years because more
women are taking fertility drugs, which release multiple eggs for
fertilization. Couples are also using in vitro fertilization, in which
doctors routinely implant more than one fertilized egg to increase the
likelihood that at least one will develop into a viable fetus.
The higher rate of multiple births after the use of
fertility drugs or in vitro fertilization also means that more
chimeric children may be found. In the United States and Canada,
fertility drugs and in vitro fertilization techniques produce
twins 28 percent of the time and triplets 6 percent of the time.
The normal rates are 1 percent and 0.013 percent
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